Issues fitting the case checker after loading

[nhribar]

I’m having some issues reloading. The case fits in my case checker before loading. But after making a round, some fit perfect, and some don’t fit at all. No consistent results. I’m using a Lee turret press with a universal expanding die, then the perfect powder measure, then bullet seating die, then crimp die.
Like I said, some fit after I’m don’t. And some don’t. I’m at a loss. I can’t find any obvious discrepancies with the calipers either.

[20X11]

Headstamp on the brass?

Edit: Also, are you using cast bullets?...this the need for the expander die?

[Shaman]

I use the Sheridan gauge which is quite intolerant. I’ve had this happen occasionally and always when using mixed head stamp range or remanufactured (from .223) brass. The only area affected at seating would be the case neck. Some brass are thicker at the neck. I suspect the brass may expand slightly during seating and cause the OD at the neck to expand just enough to fail the gauge. There’s a sticky on the site that list good and poor choices. Check your head stamps. I’ve found the list is spot on in most cases.

[Ben B.]

At a guess, you have mixed-brass converted .223/5.56 cases, and those loads that fail your case checker have thick brass walls at the neck, and those that pass do NOT have thick brass walls at the neck.

Put your calipers on the brass walls of case necks. Anything over .012” should be discarded.